Deprecate V2 API: --enable-v2 and v2v3

Flags `--experimental-enable-v2v3` and '-enable-v2' will raise a warning in 3.5,
in 3.6 they are schedule for decomissioning, such that v2store can stop be written in 3.7.

Deprecation plan in: etcd-io#12913

CHANGELOG-3.5.md

@@ -71,6 +71,7 @@ See [code changes](https://github.com/etcd-io/etcd/compare/v3.4.0...v3.5.0) and
 - [Embed Etcd.Close()](https://github.com/etcd-io/etcd/pull/12828) needs to called exactly once and closes Etcd.Err() stream.
 - [Embed Etcd does not override global/grpc logger](https://github.com/etcd-io/etcd/pull/12861) be default any longer. If desired, please call `embed.Config::SetupGlobalLoggers()` explicitly. 
 - Errors: `context cancelled` or `context deadline exceeded` are exposed as codes.Canceled, codes.DeadlineExceeded instead of 'codes.Unknown'.
+- Version 3.5 is the last version that supports V2 API. Flags `--enable-v2` and `--experimental-enable-v2v3` [are now deprecated](https://github.com/etcd-io/etcd/pull/).
 ###
 
 - Make sure [save snapshot downloads checksum for integrity checks](https://github.com/etcd-io/etcd/pull/11896).

server/embed/config.go

@@ -217,7 +217,11 @@ type Config struct {
 	InitialCluster        string `json:"initial-cluster"`
 	InitialClusterToken   string `json:"initial-cluster-token"`
 	StrictReconfigCheck   bool   `json:"strict-reconfig-check"`
-	EnableV2              bool   `json:"enable-v2"`
+
+	// EnableV2 exposes the deprecated V2 API surface.
+	// TODO: Delete in 3.6 (https://github.com/etcd-io/etcd/issues/12913)
+	// Deprecated in 3.5.
+	EnableV2 bool `json:"enable-v2"`
 
 	// AutoCompactionMode is either 'periodic' or 'revision'.
 	AutoCompactionMode string `json:"auto-compaction-mode"`
@@ -301,7 +305,10 @@ type Config struct {
 
 	ExperimentalInitialCorruptCheck bool          `json:"experimental-initial-corrupt-check"`
 	ExperimentalCorruptCheckTime    time.Duration `json:"experimental-corrupt-check-time"`
-	ExperimentalEnableV2V3          string        `json:"experimental-enable-v2v3"`
+	// ExperimentalEnableV2V3 configures URLs that expose deprecated V2 API working on V3 store.
+	// Deprecated in 3.5.
+	// TODO: Delete in 3.6 (https://github.com/etcd-io/etcd/issues/12913)
+	ExperimentalEnableV2V3 string `json:"experimental-enable-v2v3"`
 	// ExperimentalEnableLeaseCheckpoint enables primary lessor to persist lease remainingTTL to prevent indefinite auto-renewal of long lived leases.
 	ExperimentalEnableLeaseCheckpoint       bool          `json:"experimental-enable-lease-checkpoint"`
 	ExperimentalCompactionBatchLimit        int           `json:"experimental-compaction-batch-limit"`

server/embed/etcd.go

@@ -665,7 +665,9 @@ func (e *Etcd) serveClients() (err error) {
 	// Start a client server goroutine for each listen address
 	var h http.Handler
 	if e.Config().EnableV2 {
+		e.cfg.logger.Warn("Flag `enable-v2` is deprecated and will get removed in etcd 3.6.")
 		if len(e.Config().ExperimentalEnableV2V3) > 0 {
+			e.cfg.logger.Warn("Flag `experimental-enable-v2v3` is deprecated and will get removed in etcd 3.6.")
 			srv := v2v3.NewServer(e.cfg.logger, v3client.New(e.Server), e.cfg.ExperimentalEnableV2V3)
 			h = v2http.NewClientHandler(e.GetLogger(), srv, e.Server.Cfg.ReqTimeout())
 		} else {

server/etcdmain/config.go

@@ -190,7 +190,7 @@ func newConfig() *config {
 	fs.Var(cfg.cf.clusterState, "initial-cluster-state", "Initial cluster state ('new' or 'existing').")
 
 	fs.BoolVar(&cfg.ec.StrictReconfigCheck, "strict-reconfig-check", cfg.ec.StrictReconfigCheck, "Reject reconfiguration requests that would cause quorum loss.")
-	fs.BoolVar(&cfg.ec.EnableV2, "enable-v2", cfg.ec.EnableV2, "Accept etcd V2 client requests.")
+	fs.BoolVar(&cfg.ec.EnableV2, "enable-v2", cfg.ec.EnableV2, "Accept etcd V2 client requests. Deprecated in 3.5. Will be decomissioned in 3.6.")
 	fs.BoolVar(&cfg.ec.PreVote, "pre-vote", cfg.ec.PreVote, "Enable to run an additional Raft election phase.")
 
 	// proxy
@@ -262,7 +262,7 @@ func newConfig() *config {
 	// experimental
 	fs.BoolVar(&cfg.ec.ExperimentalInitialCorruptCheck, "experimental-initial-corrupt-check", cfg.ec.ExperimentalInitialCorruptCheck, "Enable to check data corruption before serving any client/peer traffic.")
 	fs.DurationVar(&cfg.ec.ExperimentalCorruptCheckTime, "experimental-corrupt-check-time", cfg.ec.ExperimentalCorruptCheckTime, "Duration of time between cluster corruption check passes.")
-	fs.StringVar(&cfg.ec.ExperimentalEnableV2V3, "experimental-enable-v2v3", cfg.ec.ExperimentalEnableV2V3, "v3 prefix for serving emulated v2 state.")
+	fs.StringVar(&cfg.ec.ExperimentalEnableV2V3, "experimental-enable-v2v3", cfg.ec.ExperimentalEnableV2V3, "v3 prefix for serving emulated v2 state. Deprecated in 3.5. Will be decomissioned in 3.6.")
 	fs.BoolVar(&cfg.ec.ExperimentalEnableLeaseCheckpoint, "experimental-enable-lease-checkpoint", false, "Enable to persist lease remaining TTL to prevent indefinite auto-renewal of long lived leases.")
 	fs.IntVar(&cfg.ec.ExperimentalCompactionBatchLimit, "experimental-compaction-batch-limit", cfg.ec.ExperimentalCompactionBatchLimit, "Sets the maximum revisions deleted in each compaction batch.")
 	fs.DurationVar(&cfg.ec.ExperimentalWatchProgressNotifyInterval, "experimental-watch-progress-notify-interval", cfg.ec.ExperimentalWatchProgressNotifyInterval, "Duration of periodic watch progress notifications.")

server/go.sum

@@ -11,6 +11,7 @@ cloud.google.com/go/firestore v1.1.0/go.mod h1:ulACoGHTpvq5r8rxGJ4ddJZBZqakUQqCl
 cloud.google.com/go/pubsub v1.0.1/go.mod h1:R0Gpsv3s54REJCy4fxDixWD93lHJMoZTyQ2kNxGRt3I=
 cloud.google.com/go/storage v1.0.0/go.mod h1:IhtSnM/ZTZV8YYJWCY8RULGVqBDmpoyjwiyrjsg+URw=
 dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
+github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
 github.com/OneOfOne/xxhash v1.2.2/go.mod h1:HSdplMjZKSmBqAxg5vPj2TmRDmfkzw+cTzAElWljhcU=

tests/go.sum

@@ -11,6 +11,7 @@ cloud.google.com/go/firestore v1.1.0/go.mod h1:ulACoGHTpvq5r8rxGJ4ddJZBZqakUQqCl
 cloud.google.com/go/pubsub v1.0.1/go.mod h1:R0Gpsv3s54REJCy4fxDixWD93lHJMoZTyQ2kNxGRt3I=
 cloud.google.com/go/storage v1.0.0/go.mod h1:IhtSnM/ZTZV8YYJWCY8RULGVqBDmpoyjwiyrjsg+URw=
 dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
+github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
 github.com/OneOfOne/xxhash v1.2.2/go.mod h1:HSdplMjZKSmBqAxg5vPj2TmRDmfkzw+cTzAElWljhcU=